x5s is a Fiddleraddon which aims to assist penetration testers in finding cross-site scripting vulnerabilities. This is not a point and shoot tool, it requires some understanding of how encoding issues lead to XSS, and it requires manual driving.

It's main goal is to help you identify the hotspots where XSS might occur by:

Detecting where safe encodings were not applied to emitted user-inputs

Release description: x5s was first and foremost designed to find encoding and character transformation issues that can lead to XSS vulnerability, and present them in a visual way where they could be reviewed with a quickness. Many tools exist for testing Web-applications to find cross-site scripting bugs. There are browser plugins, Web-scanners, and static code analyzers. We use whatever suits us in a given situation and produces the output we're interested in receiving. We developed x5s for penetration testers and other security-minded persons who already know how to find and exploit an XSS vulnerability. The tool has a slightly different bent than other tools we've used.

It's main goals include:

Automate finding the encoding issues that can lead to XSS.

Identify where character transformations occur by injecting multibyte characters such as higher Unicode code points and non-shortest form character encodings.